Various methods have been proposed for storing liquified gases, and in particular those gases, such as natural gas, which are liquified at very low temperature, in underground cavities which are made liquid-tight by the ground freezing. The liquified gas is then at about atmospheric pressure. Up to now such methods have encountered numerous difficulties, principally related to cracks which may be present in the ground before the cavity is dug or which may appear as the installation is being put into operation. Depending on circumstances, such cracks can lead either to ingress of water, which can be difficult to stop, particularly if it does not occur until after the cooling process has begun, i.e. at a time when working in the cavity is not intended, or else it can lead to gas leaking to the surface, and again such leaks are generally not detected until after the cooling process has begun, or indeed until after the installation has been put into operation.
Preferred implementations of the present invention provide a method and apparatus for storing liquified gas in an underground cavity which is sealed essentially by the ground freezing, but which avoid the drawbacks due to ingress of water or to gas leaking throughout the storage period.
In known methods, the walls of the cavity and the surrounding ground are kept under observation while the cavity is being cooled prior to filling, and during this period action is taken, when necessary, by modifying the initial cooling program and/or by reparing damage which has appeared, see French Pat. No. 2 372 752 for example.